Detects whether the specified digital sound device is available. This
function must be called _before_ install_sound().
Returns the maximum number of voices that the driver can provide, or zero
if the hardware is not present.
Detects whether the specified MIDI sound device is available. This
function must be called _before_ install_sound().
Returns the maximum number of voices that the driver can provide, or zero
if the hardware is not present.
There are two special-case return values that you should watch out for:
if this function returns -1 it is a note-stealing driver (eg. DIGMID)
that shares voices with the current digital sound driver, and if it
returns 0xFFFF it is an external device like an MPU-401 where there is no
way to determine how many voices are available.
Retrieves the hardware sound output volume, both for digital samples and
MIDI playback, as integers from 0 to 255, or -1 if the information is not
available. Parameters digi_volume and midi_volume must be valid pointers
to int, or NULL if not interested in specific value.
Retrieves the global sound output volume, both for digital samples and
MIDI playback, as integers from 0 to 255. Parameters digi_volume and
midi_volume must be valid pointers to int, or NULL if not interested in
specific value.
Initialises the sound module. You should normally pass DIGI_AUTODETECT
and MIDI_AUTODETECT as the driver parameters to this function, in which
case Allegro will read hardware settings from the current configuration
file. This allows the user to select different values with the setup
utility: see the config section for details. Alternatively, see the
platform specific documentation for a list of the available drivers. The
cfg_path parameter is only present for compatibility with previous
versions of Allegro, and has no effect on anything.
Returns zero if the sound is successfully installed, and -1 on failure.
If it fails it will store a description of the problem in allegro_error.
Call this function to specify the number of voices that are to be used by
the digital and MIDI sound drivers respectively. This must be done
_before_ calling install_sound(). If you reserve too many voices,
subsequent calls to install_sound() will fail. How many voices are
available depends on the driver, and in some cases you will actually get
more than you reserve (eg. the FM synth drivers will always provide 9
voices on an OPL2 and 18 on an OPL3, and the SB digital driver will round
the number of voices up to the nearest power of two). Pass negative
values to restore the default settings. You should be aware that the
sound quality is usually inversely related to how many voices you use, so
don't reserve any more than you really need.
Alters the hardware sound output volume. Specify volumes for both digital
samples and MIDI playback, as integers from 0 to 255, or pass a negative
value to leave one of the settings unchanged. Values bigger than 255 will
be reduced to 255. This routine will use the hardware mixer to control
the volume if it exists (i.e. the volume of all the applications on your
machine will be affected), otherwise do nothing.
Alters the global sound output volume. Specify volumes for both digital
samples and MIDI playback, as integers from 0 to 255, or pass a negative
value to leave one of the settings unchanged. Values bigger than 255 will
be reduced to 255. This routine will not alter the volume of the hardware
mixer if it exists (i.e. only your application will be affected).
By default, Allegro will play a centered sample at half volume on both
the left and right channel. A sample panned to the far right or left will
be played at maximum volume on that channel only. This is done so you can
play a single panned sample without distortion. If you play multiple
samples at full volume, the mixing process can result in clipping, a
noticeable form of distortion. The more samples, the more likely clipping
is to occur, and the more clipping, the worse the output will sound.
If clipping is a problem - or if the output is too quiet - this function
can be used to adjust the volume of each voice. You should first check
that your speakers are at a reasonable volume, Allegro's global volume is
at maximum (see set_volume() below), and any other mixers such as the
Windows Volume Control are set reasonably. Once you are sure that
Allegro's output level is unsuitable for your application, use this
function to adjust it.
Each time you increase the parameter by one, the volume of each voice
will halve. For example, if you pass 4, you can play up to 16 centred
samples at maximum volume without distortion.
If you pass 0 to this function, each centred sample will play at the
maximum volume possible without distortion, as will all samples played
through a mono driver. Samples at the extreme left and right will distort
if played at full volume. If you wish to play panned samples at full
volume without distortion, you should pass 1 to this function. Note: this
is different from the function's behaviour in WIPs 3.9.34, 3.9.35 and
3.9.36. If you used this function under one of these WIPs, you will have
to increase your parameter by one to get the same volume.
Note: The default behaviour has changed as of Allegro 4.1.15. If you
would like the behaviour of earlier versions of Allegro, pass -1 to this
function. Allegro will choose a value dependent on the number of voices,
so that if you reserve n voices, you can play up to n/2 normalised
samples with centre panning without risking distortion. The exception is
when you have fewer than 8 voices, where the volume remains the same as
for 8 voices. Here are the values, dependent on the number of voices:
1-8 voices - set_volume_per_voice(2)
16 voices - set_volume_per_voice(3)
32 voices - set_volume_per_voice(4)
64 voices - set_volume_per_voice(5)
Of course this function does not override the volume you specify with
play_sample() or voice_set_volume(). It simply alters the overall output
of the program. If you play samples at lower volumes, or if they are not
normalised, then you can play more of them without distortion.
It is recommended that you hard-code the parameter into your program,
rather than offering it to the user. The user can alter the volume with
the configuration file instead, or you can provide for this with
set_volume().
To restore volume per voice to its default behaviour, pass 1.